It is known from the prior art to harden workpieces of steel, such as tubes or blanks, or the components produced therefrom, such as for instance profiles, during or after they have undergone forming. In this case, depending on the steel material, the workpieces or components are brought to a temperature above the Ac1 or Ac3 temperature, so that a substantially austenitic microstructure is obtained, and are subsequently cooled or quenched. The martensitic microstructure thus obtained then gives the component an increased hardness, so that comparatively stable components can be produced in spite of low weight.
In particular in the industrial-scale production of hardened profiles, especially hollow profiles, in the past only comparatively simple geometries have been implemented. More complex geometries, on the other hand, can be achieved for example by the profiles being put together from a number of parts, for instance half-shells. However, the stability, weight and production process of the profile may be adversely influenced by the required connection of the parts to form a profile.
Another approach that allows components such as profiles with a more complex structure to be produced is taken by what is known as hot blowforming. In the case of hot blowforming, a hot, generally gaseous fluid is introduced under pressure by a docking punch into a hollow region of the workpiece that is sealed off by the docking punch, for instance into the interior of a tube. The fluid introduced under high pressure presses the workpiece against an outer shaping mold (known as high-pressure hydroforming) and/or the outer shaping mold is pressed against the workpiece that is under moderate pressure (known as low pressure hydroforming). In the latter case, the fluid introduced serves for fixing a certain volume in the hollow region of the workpiece, in order to allow the workpiece then to undergo forming from the outside by the mold.
If the component produced is to be hardened, the component can be hardened in a separate process step. However, this represents a comparatively cost-intensive solution for being able to provide hardened profiles with complex geometries. Therefore, the prior art has taken the approach of performing the hot blowforming and hardening in one device.
Methods and devices that are suitable for this are known for example from the prior art of DE 698 03 588 T2. It is proposed to hydroform a hollow steel workpiece with a heated pressurized medium and subsequently quench it in the forming mold, by the dominant heated medium being replaced by a pressurized cool medium.
An improvement of the production process of hardened components with complex geometries can be achieved in this way. However, it has been found that prior-art components produced in this way are not of a satisfactory quality, in particular in their end regions, that is to say where the fluids are introduced into the hollow region of the workpiece. As a result, it is particularly not possible to provide a profile that is completely hardened throughout its entire length. The workability of the workpiece in these regions is also unsatisfactory, and so premature material failure can occur. For this reason, the ends of such components or profiles are generally removed after the forming or hardening, which however leads to a high amount of reject material or scrap and consequently impairs the cost-effectiveness of the method.